Patent Document 1 is a conventional technology document that describes a structure of a sensor chip used in a conventional blood flowmeter. FIG. 13 illustrates a sensor chip of a conventional blood flowmeter described in Patent Document 1. In the conventional sensor chip illustrated in FIG. 13 includes a semiconductor laser 1 as a light emitting device, a photodiode 2 as a light-receiving element, and an optical waveguide 3 for guiding light emitted from the light emitting device in the form of divergent light, focused light, or parallel light and irradiating it toward living tissue situated outside, all of which are integrated on a single semiconductor substrate.
It further includes a shielding block 4 attached to the substrate so as to individually enclose the semiconductor laser 1 and the photodiode 2 in order to prevent light from the semiconductor laser 1 from directly entering the photodiode 2. The photodiode 2 is an edge-illuminated refracting-facet photodiode, in front of which a second light shielding board having a certain gap may be provided.
A blood flowmeter such as the above-described type measures a blood flow rate, a blood volume, a blood flow velocity, and a pulse rate by detecting interference (by heterodyne detection) between scattered light from living tissue at rest and scattered light from red corpuscles (scattering particles) moving through a capillary of living tissue (scattered light experiencing the Doppler shift Δf in accordance with the blood flow velocity). This measurement principle is described, for example, in a document by M. D. Stern: In vivo evaluation of microcirculation by coherent light scattering, Nature, vol. 254, pp. 56-58 (1975).
In order to achieve miniaturization and facilitate the assembly of individual parts, the inventors of the present invention invented a blood flowmeter equipped with a sensor unit having a structure where a light emitting device and a light-receiving element are disposed in a recess formed on a surface of a single semiconductor substrate, a cover substrate with a light shielding film for shielding undesired scattered light is disposed on an upper surface of the semiconductor substrate, light emitted from the light emitting device is irradiated toward living tissue situated outside through the cover substrate, and scattered light from the living tissue is received by the light receiving element through the cover substrate. The details are described in Patent Document 2.
Furthermore, Patent Document 3 describes a tissue blood flowmeter whose objective is to prevent a disturbance in phase of the Doppler shift due to the bombardment with the cladding of optical fiber of reflected laser light from the sample. In this tissue blood flowmeter, a pinhole is provided coaxially with the optical fiber between the optical fiber and a photoelectric conversion device, and laser light guided by the optical fiber is directed to the photoelectric conversion device through the pinhole.
Patent Document 1: Unexamined Japanese Patent Publication No. 2002-330936.
Patent Document 2: Unexamined Japanese Patent Publication No. 2004-229920.
Patent Document 3: Unexamined Japanese Patent Publication No. 2002-45342.